Objective:To assess any direct effect of extract of Paris polyphylla Simth(EPPS),a Chinese plant,on a cardiomyocyte subject to ischemia-reperfusion injury and to further elucidate its protective effect against myocardium ischemia on the cellular level.Methods:Neonatal rat cardiomyocytes were isolated and subjected to an anoxia-reoxia injury simulating the ischemia-reperfusion injury in vivo in the presence or absence of EPPS or diltizem,a positive control.The lactate dehydrogenase(LDH) activities in culture supematants and cell viabilities were analyzed using the enzymatic reaction kinetics monitoring-method and MTT method, respectively.Free intracellular calcium concentrations and activities of Na~+-K~+ ATPase and Ca~(2+) ATPase in cells were also measured with laser confocal microscopy and the inorganic phosphorus-transformation method,respectively.Results:In cardiomyocytes subject to anoxia-reoxia injury,EPPS at 50-400 mg/L showed a concentration-dependent inhibition on LDH leakage and maintenance of cell viability,and the effect was significant at 275 and 400 mg/L(both P<0.01).In addition,EPPS at 275 and 400 mg/L significantly inhibited the increase in intracellular free calcium(both P<0.01) as well as decreased the activities of Na~+-K~+ ATPase and Ca~(2+) ATPase(P<0.01,P<0.05).Conclusions:EPPS prevents anoxia-reoxia injury in neonatal rat cardiomyocytes in vitro by preservation of Na~+-K~+ ATPase and Ca~(2+) ATPase activities and inhibition of calcium overload.The direct protective effect on cardiomyocytes may be one of the key mechanisms that underlie the potential therapeutic benefit of EPPS against myocardium ischemia. Objective: To assess any direct effect of extract of Paris polyphylla Simth (EPPS), a Chinese plant, on a cardiomyocyte subject to ischemia-reperfusion injury and to further elucidate its protective effect against myocardium ischemia on the cellular level. Methods: Neonatal rat cardiomyocytes were isolated and subjected to an anoxia-reoxia injury simulating the ischemia-reperfusion injury in vivo in the presence or absence of EPPS or diltizem, a positive control. lactate dehydrogenase (LDH) activities in culture supematants and cell viabilities were analyzed using the enzymatic reaction kinetics monitoring-method and MTT method, respectively. Free intracellular calcium concentrations and activities of Na ~ + -K ~ + ATPase and Ca ~ (2+) ATPase in cells were also measured with laser confocal microscopy and the inorganic phosphorus-transformation method , respectively. Results: In cardiomyocytes subject to anoxia-reoxia injury, EPPS at 50-400 mg / L showed a concentration-dependent inhibition on LDH leakage and maintenance of cell viability, and the effect was significant at 275 and 400 mg / L (both P <0.01) .In addition, EPPS at 275 and 400 mg / L significantly inhibited the increase in intracellular free calcium (both P <0.01) as well as decreased the activities of Na ~ + -K ~ + ATPase and Ca ~ (2+) ATPase (P <0.01, P <0.05) .Conclusions: EPPS prevents anoxia-reoxia injury in neonatal rat cardiomyocytes in vitro by preservation of Na ~ + -K ~ + ATPase and Ca ~ (2+) ATPase activities and inhibition of calcium overload. The direct protective effect on cardiomyocytes may be one of the key mechanisms that underlie the potential therapeutic benefit of EPPS against myocardium ischemia.